I've recently have become more interested in portrait work and wedding photography. Im searching for a good lens that will perform well under typical wedding conditions. I've looked into the PENTAX smc DA 17-70mm f/4 AL (IF) SDM Lens but am concerned that the F/4 may not perform in low light conditions such as dark wedding receptions. I value its wide to telephoto range. I'd supposed the 16-50mm f/2.8 would be a better choice. Why is it that canon and Nikon have lenses that seem to have a wide - telephoto range but Pentax always has wide-50mm then 50-300mm Cant we just find an in between?

There is a couple reason into it. First you're right, it is about f/2.8, which is better in low light condition, or it allows u to shoot with lower ISO for better image quality.

The second reason will be the built quality. Many times in wedding photography, u will be in pretty tight space, either because of the small room or crowds around you. Often, your lenses will hit something. With built quality of 16-50mm, it will survive longer.

Other Pentax pro grade lens that I recommend to complement this lens is DA* 50-135mm f/2.8

To answer your question why Pentax seems to have a weird zoom length.. the answer is actually they are very rational in the lens focal length decisions.

When Pentax goes into digital era. they decided to stick with APS-C sensor (1.5x crop factor) and then invested quite heavily in making DA, DA Limited and DA* lenses which is optimized for their digital SLR cameras.

Because they don't have any idea or don't decide on making full frame (perhaps in the future or not at all). They try to mimic the focal length that are popular in film era.

For example, 16-50mm will closely 24-75mm
50-135 will closely equivalent to 75-200mm

On the other hand, Canon is planning to have full frame camera out, so they are releasing lenses for that purpose. So called "L" lenses.

16-35mm f/2.8, 24-70mm f/2.8, 70-200mm f/2.8, 24-105mm f/4 and so on.

Those lenses inevitably become very popular among crop sensor camera users in the last 4-5 years.

Now that many photographers are getting used to Canon or Nikon lenses, Pentax decision on focal length might seems weird, but it is not.

I wrote Canon vs Pentax lenses at my blog a while ago, probably this will be helpful for you to check out what Pentax has available especially in high-pro grade prime and pro grade zoom area.

I've recently have become more interested in portrait work and wedding photography. Im searching for a good lens that will perform well under typical wedding conditions. I've looked into the PENTAX smc DA 17-70mm f/4 AL (IF) SDM Lens but am concerned that the F/4 may not perform in low light conditions such as dark wedding receptions. I value its wide to telephoto range. I'd supposed the 16-50mm f/2.8 would be a better choice. Why is it that canon and Nikon have lenses that seem to have a wide - telephoto range but Pentax always has wide-50mm then 50-300mm Cant we just find an in between?

Find the Sigma 30mm f/1.4 or FA 35mm f/2. I find it easier just to work with a smaller lens at these types of situations.

Wow you guys! Thanks for that very informative answer. I think I may end up with the 16-50mm in the end or perhaps I should keep an eye out for some primes like GXLR suggested as well. Because of buget reasons I'll have to hold off on a new the 50-135mm. My tamron 70-300 will have to do for now... Thanks again for your responces.

Did you consider FA and FA* lenses, they are predecessor of DA and DA* where FA are consumer and FA* pro grade. I was reading much about those and saw many pictures and the IQ is amazing. The only thing is that they don't have weather sealing and SDM, but I don't think you need that for weddings anyway.

This is the FA line up with the date when it was introduced, and none of them is discontinued

Wow Nelepl Thank you for that list. I will look into some of those. Yeah my Pentax F 35-80mm SMC is pretty much a piece of garbage. The build quality is awful.. feels like its going to fall apart and the worse for Chromatic Aberration. I heard the F series are bad for that just like the FAJ series being pretty low quality as well. Thanks again

Docrjay you got me thinking about the 50-135 DA now... I've also seen some recomendations for the SIGMA 50-150 F2.8 II APO EX DC which retails here in canada for 1000 (ebay 700)... the Pentax 50-135 DA* is going for 1199.. really when Im spending that kind of money an extra 120 really doesnt matter plus id be getting a wheather sealed lens. Still.. what are anyones thoughts on the Sigma?

buying sigma is a great way to reduce cost. The built quality is very good, focusing is also very good, maybe even faster than SDM.

The catch will be image quality (slightly worse especially in the corner, but in wedding type of photo, a bit of corner softness does not matter to me) and quality control, it is wise to buy from reputable sellers that accept return/exchange if you buy Sigma.

Wow Nelepl Thank you for that list. I will look into some of those. Yeah my Pentax F 35-80mm SMC is pretty much a piece of garbage. The build quality is awful.. feels like its going to fall apart and the worse for Chromatic Aberration. I heard the F series are bad for that just like the FAJ series being pretty low quality as well. Thanks again

You just got a bad F lens.

Most of the FA lenses are just rebranded F lenses. i.e. 300mm f/4.5, 600mm f/4

If I would be spending that kind of money this is what I would buy, it is worth couple of hundred bucks moresmc PENTAX FA * 80-200mm f/2.8 IF ED

Can you prove it with pictures? From what I have seen, the DA* has better color rendering and sharpness.

I wouldn't suggest a 80(70)-200mm for weddings. I have tried to see if this was possible at a gathering (didn't go past 70mm unless I had to (experiment)). It is really hard to stand back at 70mm (let alone 80mm), so consider possibly just a set of primes. You can find the FA 135mm, 50mm f/1.4, 35/30mm f/1.4/2 real easily and makes a great combo.

Im thinking docrjay is probably right with his suggestion. I can get by with the kit lens for my wide angle for now. The 50-135 DA is very high rated. I wont be able to buy a new body for quite sometime though.... Im getting married in 6 months and have 480ppl coming to my wedding so first things first... If I put a little away I should be able to aford the 50-135 by April. Until I decide to open my own business or until i win the lottery ill have to make due with what i've got. Perhaps in the near future I can pick up a K10D or something at a good price or just break down and get the K7....Thanks to everyone for your help.